The present invention relates to a metal sealing cap especially suitable for closure of contaners with contents developing high inner pressure. More particularly, the invention relates to caps of the variety in which a cap lower part is removable from a cap upper part by means of a tear-off band, said tear-off band being used to connect the sealing cap securely to the container by flanging in, and in which the cap upper part is removably applicable to the container for reclosing the container, once the line of weakened strength connecting the cap upper part to the cap lower part has been ruptured.
Various metal sealing cap constructions are known, consisting of upper and lower cap parts which can be separated from each other with aid of a tear-off tab running along one or more lines of weakened strength. In some of these constructions, the lower cap part is securely connected to the container to be sealed, by flanging in or by contracting, and it remains on the container. In other constructions, as when only one line of weakened strength is provided and the entire lower cap part is a tear-off band, then the lower cap part is completely removed from the container upon initial opening of the pressure cap. The upper cap part is reusable, i.e., it is removably applicable to reclose the container, once the cap has been opened by tearing off the lower cap part.
Such sealing caps are intended to show that the container has been open. The intact condition of the whole cap guarantees the consumer the original contents of the container. Such a cap also ensures that contents of containers developing high inner pressure have been sealed satisfactorily; however, once the cap has been opened, the reapplied cap upper part no longer has the same ability to withstand inner pressure.
A sealing cap of the first-mentioned type is known, for example, in German published application 1,956,586 (Offenlegunschrift) where several individual thread segments are provided as a multiple-thread finish in the cap upper part, for engagement with a corresponding number of thread formations on the outside of the container finish. The thread segments on the sealing cap coact with the threads on the container in such manner that the cap-thread segments are located between the container-thread parts in a sealed condition while and after making the initial closure operation. Thus, the cap-thread segments and the container-thread parts, being in circumferential clearance and not in contact with each other, cannot interfere with or hinder the slightly rotational action of the cap before being axially pressed against the bottle, as roll action proceeds to flange in the cap lower part, to secure a sealed closure of the bottle.
Independent of the fact whether the cap upper part intended for later re-closing of the container is constructed as a screw cap or as a clinch cap, the disadvantage with closure caps of this known type to date is that a weakened edge is created upon tearing off the tear-off band along the line of weakened strength at the lower edge of the skirt of the cap lower part. Score formations which have thus far been applied at the lower region of the skirt of the cap upper part near the line of weakened strength do not reliably and sufficiently stiffen the skirt of the cap upper part to completely prevent the skirt from becoming deformed in the course of tearing the tear-off band; effective reusability of the cap is thus degraded or impaired. In the case of threaded caps, thread formations on the cap upper part tend to overturn because the cap has become oval due to the lack of sufficient stiffness in the cap skirt. On the other hand, the material thickness of the cap material cannot be selected in such thickness as to avoid such mishaps.
There is the further disadvantage that after removal of the tear-off band along the line of weakened strength on the lower edge of the skirt of the cap upper part, a sharp edge is created which can cause cuts or injuries to the consumer when reusing the cap upper part; this is particularly the case for threaded caps in which a turning motion between the fingers is required for reclosure.